1. Field of the Invention
The present invention relates to an agent increasing the rate of hardening of cements, mortars and concretes while maintaining their workability.
It also concerns an adjuvant for cements, mortars and concretes, comprising an effective quantity of said agent, together with the cements, mortars or concretes comprising an effective quantity of said agent or of said adjuvant.
Within the scope of the present invention a rate of hardening is intended to mean the time elapsing between the beginning and the end of setting of the cements.
The standardized measurement method used to obtain this rate of setting is based on the change, as a function of time, in the coefficient of penetration of the needle of a setting tester.
Still within the scope of the present invention, workability of the cements, mortars or concretes is intended to mean the ability to maintain a rheological state in which the cements, concretes and mortars can be handled, that is to say in particular can be poured or pumped without appreciable alteration in their other properties. What is wanted is that this workability should at least be maintained from the end of the mix until the time when the mortars and concretes are placed in position.
2. Related Art Statement
Portland cements, or their analogs, are known to endow mortars and concretes which contain them with high mechanical characteristics after hardening. However, as a result of their essential constituent, which is tricalcium aluminate, these cements result in an onset of setting and a setting time which are frequently judged to be too long in certain uses.
In fact, in the case of applications in the building trade field, attempts are made not only to extend the period for which the workability is maintained, but above all, every effort is made to meet the requirements of working rates at the work sites. As a result, it is imperative that, after approximately 16-17 hours following their being placed in position, in other words in what has conventionally become known as "early age", the concretes and mortars should have sufficient mechanical strength to permit various operations such as, for example, the removal of shuttering. Further, it is not inappropriate to emphasize that the performance required where mechanical strength after 16-17 hours is concerned is increasingly high.
Many products have been proposed as additives for mortars and concretes in order to improve their characteristics.
Thus, various setting accelerators have been proposed, these products being chosen especially from chlorides, sulfates, nitrates and others. However, it is now recognized that their use gives rise to other problems including in particular phenomena of corrosion of the metal reinforcements of reinforced concretes into which they are incorporated.
To try and meet the various requirements of the art, that is to say essentially to obtain an increase in the rate of hardening while maintaining good workability, it might have been envisaged to add such setting accelerators only at the time of the placing of the concretes or mortars in position, or only a few minutes before this operation. This would have made it possible to maintain good workability of the mortars and concretes while obtaining an acceleration in their rate of hardening and therefore a satisfactory strength in the early age. Nevertheless, resorting to this type of solution entails heterogeneities in the concretes and as a result gives rise to large differences where their mechanical strength is concerned.
It has also been envisaged to use, in combination with these additives which have an accelerating effect on setting, setting-retarding agents such as gluconates, the effect of the latter additives compensating or moderating the effect of the former. However, resorting to such mixtures results almost unavoidably in problems of false setting, which produce serious disadvantages at the time of the removal of shuttering from the concretes in the early age.
These disadvantages exhibited by the various solutions tested and employed according to the prior art were aggravated further by segregation or bleeding problems appearing when, in order to meet technical requirements, fluid mortars or concretes had been used, that is to say hydraulic binders with a water-to-cement (W/C) ratios higher than 0.5 and in most cases between 0.6 and 0.7.
Consequently, no agent or no adjuvant has so far made it possible to increase the rate of hardening of hydraulic binders so as to make it possible to obtain satisfactory mechanical strength approximately 16 to 17 hours after their being placed in position, without, however, detriment to their workability.
Now, the Applicant Company has had the merit of finding, at the outcome of numerous investigations, an agent which makes it possible to maintain or even to improve the workability while increasing the rate of hardening of cements, mortars and concretes.